Re: [Xen-devel] [PATCH v4 2/4] x86: track when in NMI context

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.02.2020 13:19, Roger Pau Monne wrote:
> Add helpers to track when running in NMI handler context. This is
> modeled after the in_irq helpers.
> 
> The SDM states that no NMI can be delivered while handling a NMI
> until the processor has executed an iret instruction. It's possible
> however that another fault is received while handling the NMI (a #MC
> for example), and thus the iret from that fault would allow further
> NMIs to be injected while still processing the previous one, and
> hence an integer is needed in order to keep track of in service NMIs.
> The added macros only track when the execution context is in the NMI
> handler, but that doesn't mean NMIs are blocked for the reasons listed
> above.
> 
> Note that there are no users of in_nmi_handler() introduced by the
> change, further users will be added by followup changes.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

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